Method of Polishing the Inner Peripheral End Surfaces of Substrates for a Recording Medium Using a Brush

ABSTRACT

The object of the invention is to provide a method of polishing the inner peripheral end surfaces of substrates while maintaining a sufficiently high working precision at the time of polishing the inner peripheral end surfaces of a plurality of disk-like substrates for a recording medium. According to the invention, there is provided a method of polishing the inner peripheral end surfaces of disk-like substrates for a recording medium using a brush comprising: providing a plurality of disk-like substrates for a recording medium having a circular hole at the central portion thereof thereby forming an inner peripheral end surface, and stacking them while aligning the circular holes to form an object to be polished having the circular hole at the central portion thereof; bringing a polishing material slurry containing a polishing material into contact with the object to be polished; and inserting a polishing brush having brush hairs studded on the periphery of a rod-like shaft into the circular hole of the object to be polished in a state where the slurry is brought into contact with the object to be polished, and rotating the polishing brush with the shaft as a center axis to polish the inner peripheral end surfaces of the substrates; wherein the polishing material slurry is controlled to remain at a constant temperature.

CROSS REFERENCE TO RELATED APPLICATION

This application is an application filed under 35 U.S.C. §111(a)claiming benefit pursuant to 35 U.S.C. §119(e) of the filing date ofProvisional Application No. 60/606,882, filed on Sep. 3, 2004, pursuantto 35 U.S.C. §111(b).

TECHNICAL FIELD

The present invention relates to a method of polishing the innerperipheral end surfaces of substrates for a recording medium and amethod of producing the substrates by using the above method, etc.

BACKGROUND ART

An aluminum substrate has been widely used as a substrate for a magneticrecording medium such as a magnetic disk. As the magnetic disks arebeing produced in smaller sizes and smaller thickness but record data ata higher density, an aluminum substrate is being gradually replaced by aglass substrate having superior surface flatness and substrate strength.As glass substrates for magnetic recording medium, there have been usedchemically reinforced glass substrates for enhancing the substratestrength and crystallized glass substrates featuring increased substratestrength based on the crystallization.

Accompanying the trend toward high-density recording, further, themagnetic head is being changed from a thin-film head to amagneto-resistive head (MR head) and to a giant magneto-resistive head(GMR head). It is therefore expected that reproducing the contents ofthe magnetic recording medium of the glass substrate by usingmagneto-resistive heads will become standard in the future.

Thus, a variety of improvements have been made to the magnetic disk forhigh-density recording. Advances in the magnetic disk, however, are alsoaccompanied by new problems concerning the glass substrate for themagnetic recording medium. One of them is to properly clean the surfacesof the glass substrate. That is, adhesion of a foreign matter on thesurfaces of the glass substrate could become a cause of defects in thethin film formed on the surfaces of the glass substrate or a cause ofprotuberances formed on the surfaces of the thin film. Further, inreproducing the contents of the magnetic recording medium on the glasssubstrate by using a magneto-resistive head, if the flying height(floating height) of the head is lowered to increase the recordingdensity, there may often occur erroneous reproducing operation or aphenomenon that the reproduction is not accomplished. The cause stemsfrom the protuberances that are formed on the surface of the magneticdisk due to particles on the glass substrate turning into thermalasperity, generating heat in the magneto-resistive head, varying theresistance of the head, and adversely affecting the electromagneticconversion.

A principal cause of foreign matter on the surface of the glasssubstrate for the magnetic recording medium described above is that theend surface of the glass substrate is not smooth and, hence, the endsurface abrades the wall surface of a resin casing, whereby resin orglass particles formed by the abrasion, as well as other particlestrapped on the inner peripheral end surface and the outer peripheral endsurface of the glass substrate, adhere to the surfaces.

Patent document 1 (JP-A-11-221742) discloses a polishing method whereina disk-like glass substrate (substrate for a recording medium) having acircular hole at the central portion is immersed in a polishing solutioncontaining free grains, and the end surfaces of the glass substrate arepolished by being brought into rotational contact with a polishing brushor a polishing pad by using a polishing solution containing the freegrains.

When the inner peripheral end surface of the substrate is to be polishedby using the above slurry and the polishing brush, the polishing iseffected by rotating the brush while dripping the slurry onto the centerhole of the object to be polished which is formed by stacking aplurality of pieces of substrates aligned with the center holes of otherdisk-like substrates having center holes, or inserting a rod-likepolishing brush in the center hole in a state where the object to bepolished is immersed in the slurry. According to this polishing method,however, the temperature rises due to the friction with the object to bepolished, the polishing material slurry and the polishing brush. Therise in temperature causes the rate of polishing to vary and makes itdifficult to conduct the polishing while maintaining a correct amount ofworking. On the other hand, a stack of substrates have been chamfered atthe end surfaces and form dented portions at the chamfered portionsamong the upper and lower substrates. A difficulty is involved if it isattempted to polish the dented portions maintaining the same workingprecision as for other end surfaces. It is desired to enhance thedimensional precision of the center holes of the disk-like substratesfor a recording medium. Therefore, it is necessary to enhance theworking precision in polishing the inner peripheral end surfaces.

[Patent document 1] Japanese Unexamined Patent Publication (Kokai) No.11-221742

DISCLOSURE OF THE INVENTION

It is, therefore, an object of the present invention to provide a methodof polishing the inner peripheral end surfaces of substrates whilemaintaining a sufficiently high working precision at the time ofpolishing the inner peripheral end surfaces of a plurality of disk-likesubstrates for a recording medium.

The present invention provides a method of polishing the innerperipheral end surfaces of disk-like substrates for a recording mediumand a method of producing the substrates by using the method describedbelow.

(1) A method of polishing the inner peripheral end surfaces of disk-likesubstrates for a recording medium using a brush comprising:

providing a plurality of pieces of disk-like substrates for a recordingmedium having a circular hole at the central portion thereof therebyforming an inner peripheral end surface, and aligning and stacking thecircular holes to form an object to be polished having the circular holeat the central portion thereof;

bringing a polishing material slurry containing a polishing materialinto contact with the object to be polished; and

inserting a polishing brush having brush hairs studded on the peripheryof a rod-like shaft into the circular hole of the object to be polishedin a state where the slurry is brought into contact with the object tobe polished, and rotating the polishing brush with the shaft as a centerto polish the inner peripheral end surfaces of the substrates;

wherein the polishing material slurry is controlled to remain at aconstant temperature.

(2) The method of polishing using a brush according to (1) above,wherein the polishing brush is rotated and is reciprocally moved in adirection of inserting the brush relative to the object to be polishedto effect the polishing.

(3) A method of producing disk-like substrates for a recording mediumincluding a step of effecting the method of polishing using a brushaccording to (1) or (2) above.

(4) A substrate produced by the method of producing disk-like substratesfor a recording medium according to (3) above.

(5) A method of producing a magnetic recording medium including a stepof effecting the method of polishing using a brush according to (1) or(2) above.

According to the polishing method of the present invention whichcontrols the temperature of the polishing material slurry to remainconstant, it is made possible to maintain constant the rate of polishingthe inner peripheral end surfaces of the substrates and, hence, toeffect the polishing while maintaining a high dimensional precision.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view of a polishing device that can be usedin the polishing method of the present invention.

FIG. 2 is a cross-sectional view of the substrates that are stacked.

-   1 polishing device container-   2 holding plate-   3 substrate holder-   4 rotary brush for polishing-   5 rotary drive unit-   6 polishing material slurry flow port-   7 polishing material slurry-   8 substrate-   9 temperature sensor-   10 chiller/temperature controller-   11 slurry pipe-   12 filter-   13 cooling tank-   14 pump-   15 stirrer-   16 cooling water pipe-   100 polishing device

BEST MODE FOR CARRYING OUT THE INVENTION

The polishing method of the present invention is to simultaneouslypolish the inner peripheral end surfaces of a plurality of pieces ofdisk-like substrates, for a recording medium and that are stacked, byusing a slurry which contains a polishing material and a polishing brushhaving hairs studded on the periphery of the rod. FIG. 1 is across-sectional view schematically illustrating a polishing device thatcan be used in the polishing method of the present invention. Apolishing device 100 includes a polishing device container 1, a holdingplate 2, a substrate holder 3 installed on the holding plate 2, a rotarybrush 4 for polishing, and a rotary drive unit 5. The interior of thepolishing device container 1 is filled with a polishing material slurry7. The brush 4 is brought into rotational contact with the innerperipheral end surfaces of the substrates 8 by using the polishingmaterial slurry 7 that flows through a polishing material slurry flowport 6 and through the inside of the substrate holder 3. In this device100, the substrates are immersed in the polishing material slurry 7, sothat the substrates come in contact with the slurry 7.

In the method of the present invention, the temperature of the slurry 7is maintained constant so as to maintain the rate of polishing constant.The temperature of the slurry 7 is measured by a temperature sensor 9associated with a chiller unit/temperature controller 10, and the slurryis cooled in the cooling tank 13 so as to keep its temperature at apreset temperature. The slurry 7 from the polishing device 100 passesthrough a slurry pipe 11 and is, preferably, filtered through a filter12 where substances produced by the polishing are removed and, then,enters into the cooling tank 13. The cooling tank 13 is of a doublestructure holding the slurry 7 in the inner side and circulating thecooling water in the outer side through a cooling water pipe 16. Astirrer 15 is provided in the cooling tank 13 to maintain thetemperature of the slurry uniform and to prevent the polishing materialfrom precipitating in the slurry. The temperature of the cooling tank 13is controlled by adjusting a temperature of a predetermined amount ofcooling water, by adjusting a flow rate of cooling water to apredetermined temperature, or by adjusting both the amount and thetemperature of the cooling water. The slurry 7 controlled to apredetermined temperature is returned back to the polishing device 100through a pump 14. Thus, the temperature of the slurry 7 is maintainedconstant at the time of polishing. The temperature of the slurry 7 maybe maintained constant to maintain the rate of polishing constant andmay be at any temperature.

Next, FIG. 2 is a cross-sectional view of substrates that are stacked toform an object to be polished. An inner peripheral end surface 21 ofeach substrate is constituted by an end edge surface 22 and chamferedportions 23. A dented portion 24 is formed by the chamfered portions 23at the end surfaces 21 between the upper and lower substrates. Thedented portion 24 hardly comes into contact with the brush 4 andreceives little contact pressure, to account for inferior polishing ofthe edge surfaces 22. Therefore, favorable and precise polishing can beeffected if the brush 4 is moved up and down relative to the stack ofsubstrates forming the object to be polished in addition to beingrotated. The up-and-down motion can be realized by moving the brush 4 upand down or by moving the substrate holder 3 up and down.

In the present invention, the “up” and “down” directions are based onthe upper and lower directions in FIG. 1.

There is no particular limitation on the polishing material or on theslurry that are used in the polishing method of the present invention,and there can be used any polishing material and any polishing materialslurry that have been known in this field. Concretely, there can be usedsuch polishing materials as rare earth oxide, iron oxide, zirconiumoxide or silicon dioxide. To polish the surfaces of the glasssubstrates, there can be used a polishing material containing rare earthoxide and, particularly, cerium oxide as a chief component on account ofits polishing rate that is several times superior to that of iron oxide,zirconium oxide or silicon dioxide. Described below is a polishingmaterial slurry including cerium oxide though this is not intended toimpose any limitation.

The polishing material slurry can be obtained by dispersing in water thepolishing material which contains, as a chief component, a rare earthoxide containing cerium oxide. The slurry may contain a dispersingagent, a chelating agent and the like as required.

As the polishing material comprising chiefly a mixture of rare earthoxides containing cerium oxide that is to be contained in the polishingmaterial slurry, there can be exemplified a low-cerium polishingmaterial of the bastnaesite type, containing cerium oxide in an amountof about 50% by mass, or of the chlorinated rare earth type, ahigh-cerium polishing material of the synthetic type containing ceriumoxide in an amount of 70 to 90% by mass, and a highly pure cerium oxidecontaining cerium oxide in an amount of not lower than 99% by mass.

The bastnaesite-type polishing material is obtained by pulverizing thebast naesite which is a fluorinated carbonate mineral of rare earthelements and by conducting the steps of chemical treatment, drying,roasting, milling, classifying and finishing. The bastnaesite typepolishing material contains about 50% by mass of cerium oxide and,further contains, other rare earth elements as basic fluorides, such asLaOF, NdOF, or PrOF. The chlorinated rare earth type polishing materialis obtained by forming a hydroxide cake of a chlorinated rare earth,drying it, roasting it as a partial sulfate, followed by milling,classifying and finishing, and contains cerium oxide in an amount ofabout 50% by mass as well as other rare earth elements as basicanhydrous sulfates, such as La₂O₃.SO₃, Nd₂O₃.SO₃ and Pr₅O₁₁.SO₃.

A high-cerium polishing material of the synthetic type is obtained byroasting a starting material such as bastnaesite, dissolving it by usingnitric acid, heating it while adjusting the pH with a dilute ammoniawater to hydrolyze Ce⁴⁺ to form a hydroxide thereof, and conducting thesteps of filtering, drying, roasting, milling, classifying andfinishing, and contains cerium oxide in an amount of 70 to 90% by mass.The highly pure cerium oxide is obtained by dissolving an oxidized rareearth in a nitric acid, extracting Ce⁴⁺ existing in an aqueous solutionwith tributyl phosphate-benzene to transfer it into an organic phase,reversely extracting it with an aqueous phase containing a reducingagent such as sodium nitrite to form cerium oxalate, followed byroasting. The purity of cerium oxide usually becomes as high as not lessthan 99.9% by mass.

The cerium oxide has a Moh's hardness of 5.5 to 6.5 which is equal to,or slightly higher than, the Mohs' hardness of a glass, and which can befinely adjusted. Therefore, the cerium oxide can be favorably used as amaterial for polishing glass. Both the low-cerium polishing material andthe high-cerium polishing material have excellent polishing power. Here,however, the high-cerium polishing member has the feature of aparticularly long life. Though there is no particular limitation on theparticle size of the polishing material comprising chiefly a mixture ofrare earth oxides including cerium oxide used for the polishing materialcomposition, there can be preferably used a polishing material havingparticle sizes corresponding to a cumulative value of 50% of volumedistribution of 0.5 to 3 μm as measured in compliance with JIS R 6002,“6. Method of Testing Electric Resistance”. It is desired that thecrystal system of the cerium oxide is a cubic system.

The polishing material slurry may contain a chelating agent, asrequired. When the chelating agent is contained, the reactivity of theglass component formed by polishing can be lowered. In conventionalpolishing of the glass surfaces for finishing, the polishing materialslurry is usually used by being circulated. As the polishing materialslurry is used for extended periods of time, however, the glasscomponent which is the object to be polished gradually increases in theslurry that is used by being circulated. If the glass componentuniformly covers the surfaces of the polishing material particles, notonly the precipitate of the polishing material becomes very hard butalso the precipitate of the polishing material deposits thereon againdue to its high affinity to the glass surfaces, deteriorating theability of the glass to be washed.

If the polishing material slurry contains a chelating agent, thereactivity drops between the surfaces of the polishing materialparticles and the surfaces of the glass, and the surfaces of thepolishing material particles are prevented from being covered with theglass component. As a result, no hard precipitate forms and thedeterioration of an ability to be washed is inhibited. Preferredconcrete examples of the chelating agent include o-phenanthroline,gluconic acid and a salt thereof, amino acid andethylenediaminetetraacetic acid. As the gluconic acid and the saltthereof, there can be exemplified a gluconic acid and a sodium salt, acalcium salt, a zinc salt and a ferrous salt thereof.

There is no particular limitation on the amino acid that is contained,and there can be used, for example, an acidic amino acid, a neutralamino acid, a basic amino acid, metal salts thereof, and compounds inwhich hydrogen atoms of the amino group of the amino acid are partlysubstituted with an alkyl group, a hydroxylalkyl group or an alkoxylgroup. However, if the polishing material slurry becomes acidic, thechemical effect of the cerium oxide itself, for polishing the glass,drops and the working speed decreases. When the acidic amino acid is tobe used, therefore, it is desired to also use a basic amino acid incombination. Further, the amino acid may be either the one thatnaturally exists or one that is synthesized. Moreover, the amino acidhaving an optical isomer may be either of the D-type or the L-type.

As the amino acid that can be used for the polishing material slurry,there can be exemplified glycine, alanine, valine, leucine, isoleucine,cerin, threonine, cysteine, cystine, methionine, aspartic acid, glutamicacid, lysine, alginine, phenylalanine, tyrosine, histidine, tryptophane,proline, hydroxyproline, diiodotyrosine, thyroxine, hydroxylysine,β-alanine, γ-aminobutyric acid, anthranilic acid, m-aminobenzoic acid,and p-aminobenzoic acid. Among them, glycine and alginine can beparticularly preferably used. The amino acid can be used in one kindalone or in two or more kinds in combination.

Among the above chelating agents, it is desired to use o-phenanthrolineand gluconic acid as well as a salt thereof. It is desired that thecontent of the chelating agent is 0.05 to 0.3% by mass. When its contentis smaller than 0.05% by mass, the effect of suppressing the reactivityof the glass component is poor. When its content exceeds 0.3% by mass onthe other hand, the polishing rate decreases.

The polishing material slurry can further contain an acetonato complexof aluminum having 1 to 3 acetonato ligands. When the acetonato complexof aluminum is contained, the polishing material is suppressed fromadhering to the glass substrate or to the polishing device, and loweringof the ability to be washed is prevented. Usually, the polishingmaterial is a super fine powder having an average particle size of about1 to about 2 μm. Due to its surface activity, the polishing materialexists while being aggregated in the polishing slurry. The aggregatedparticles lower the apparent surface area and suppress the polishingmaterial from adhering onto the glass substrate and the polishingdevice. However, the particles on the outermost shell maintain theiractivity. Once adhered to the glass substrate and the polishing device,the particles can no longer be removed by washing such as by runningwater or an ultrasonic application. The ordinary polishing materialtends to adhere onto the glass substrate and the polishing device.Contrary to this, the polishing material containing the acetonatocomplex of aluminum does not adhere due to the interaction between theacetonato complex of aluminum and the aggregated particles of thepolishing material in the polishing material slurry, preventing loweringin the ability to be washed.

Concrete examples of the acetonato complex of aluminum that is usedinclude a complex having an acetyl acetonate (R=methyl) ligand such asaluminum tris(acetylacetonate) and a complex having an ethylacetoacetate (R=ethoxy) ligand such as aluminum tris(ethylacetoacetate). Among them, it is desired to use aluminumtris(acetylacetonate). The acetonato complex of aluminum may be the onehaving two or three kinds of different acetonato ligands in a molecule.Further, the acetonato complex of aluminum may be used in a single kindor in two or more kinds in combination. It is desired that the contentof the acetonato complex of aluminum is 0.05 to 0.3% by mass. When thecontent is smaller than 0.05% by mass, the effect of preventing theadhesion to the polishing material is poor. When the content exceeds0.3% by mass, on the other hand, the polishing rate decreases.

To improve the dispersion of particles, to prevent sedimentation and toimprove workability, the polishing material slurry may be furtherblended, as required, with glycols such as ethylene glycol andpolyethylene glycol, phosphates such as tripolyphosphate andhexametaphosphate, polymeric disperants such as polyacrylate, celluloseethers such as methyl cellulose and carboxymethyl cellulose, andwater-soluble polymers such as polyvinyl alcohol. The amount of theiraddition to the polishing material is, usually, 0.05 to 20% by mass,preferably, 0.1 to 15% by mass and, more preferably, 0.1 to 10% by mass.

The polishing material slurry is usually used while being dispersed in adispersant such as water at a concentration of about 5 to 30% by mass.As the dispersant, there is used water or a water-soluble organicsolvent. As the water-soluble organic solvent, there can be exemplifiedalcohol, polyhydric alcohol, acetone and tetrahydrofuran. Water,however, is usually used. It is also allowable to add an assistant thatis usually used for an ordinary cerium oxide polishing material.

The slurry used in the method of the present invention may be obtainedby mixing starting materials together and has no particular limitation.Desirably, however, the slurry may be mechanically mixed and prepared atthe above mixing ratio by using a ball mill or a high-speed mixer.

The end surfaces of the substrates are usually polished after a circularhole at the centers of the glass substrates is formed and the innerperipheral end surfaces and the outer peripheral end surfaces arechamfered. Thereafter, the substrates may be polished on the recordingsurfaces thereof and, as required, are, further, chemically strengthenedby using a chemical strengthening solution such as potassium nitrate orsodium nitrate.

On the thus fabricated substrates, there are successively overlaid anunderlying layer, a magnetic layer, a protection layer and a lubricatinglayer to produce a magnetic recording medium. As the underlying layer,there can be usually used a nonmagnetic material such as Cr, Mo, Ta, W,V, B or Al though this is not to impose any limitation. As the magneticlayer, there can be used a magnetic film comprising chiefly Co. As theprotection layer, there can be used a Cr film or a carbon film. Thelubricating layer is formed by diluting a perfluoroether which is aliquid lubricant with a fluoro-type solvent, applying it and drying it.

EXAMPLES

The method of the present invention will be described in further detailby way of an Example which, however, is not intended to limit theinvention.

Example 1

150 pieces of glass substrates (TS-10SX manufactured by Ohara Co.) for ahard disk (HD) each having a diameter (outer diameter) of 65 mm, adiameter (inner diameter of the center hole) of 20 mm and a thickness of0.635 mm, were stacked and were subjected to the polishing on theirinner peripheral end surfaces by using a polishing device shown in FIG.1 under the conditions described below. The inner peripheral end surfaceof the substrate included an end edge surface of 0.335 mm and chamferedportions of 0.150 mm on both sides thereof.

1. Polishing:

1.1. Polishing Material Slurry.

Kind of polishing material, grain size: cerium oxide (SHOROX A-10manufactured by Showa Denko Co.), average particle size, 1.4 μm.

Dispersion medium: water

Dispersing agent: sodium hexametaphosphate

Concentration of polishing material in the slurry: 10% by mass

Material of brush, length of hair, diameter of hair:

nylon, 4 mm, φ 0.15 mm.

Rotational speed of brush: 2400 rpm

Polishing time: 20 min.

The temperature of the polishing slurry was controlled to be 25° C. byusing a mechanism shown in FIG. 1.

Comparative Example 1

The polishing was conducted in the same manner as in Example 1 above butwithout controlling the temperature. The temperature was 26° C. at thestart of the polishing but was elevated to 30° C. at the end of thepolishing.

2. Testing for Evaluation.

2.1. Observing Defects on the Surface.

The substrates polished in Example and in Comparative Example above wereobserved for defects on the surfaces. The surfaces were observed alongthe whole inner peripheral end surfaces by using a microscopemanufactured by Olympus Co. at a magnification of 200 times.

2.2. Inspecting the Sizes of the Inner Peripheral End Surfaces.

A total of three substrates were measured for their sizes including twosubstrates of the outermost sides and one substrate at the center thatwere polished in Example and in Comparative Example above. The resultswere as shown in Table 1 below. The results are average values of thesizes of the three substrates. TABLE 1 Example 1 Comparative Example 1Polishing temp. (° C.) 25° C. (constant) 26 to 30° C. Inner diameter19.995 19.995 before polished (mm) Inner diameter after 20.011 20.014polished (mm) Amount polished (μm) 16 19

From the above results of testing, it was confirmed that the surfaceswere observed to contain no scars or no pits in both Example 1 andComparative Example 1. As for the sizes of the inner peripheral endsurfaces, the polishing amount was 16 μm as expected in Example 1whereas the polishing amount was 19 μm in Comparative Example 1, whichwas larger by 3 μm than the expected amount. By controlling thetemperature to remain constant at the time of polishing, the rate ofpolishing (rate of working) becomes stable, and there is obtained theinner diameter which is nearly the same as the target value. Thisfurther suppresses dispersion in the inner diameter caused by a changein the hardness of the brush stemming from local elevation of thetemperature.

1. A method of polishing the inner peripheral end surfaces of disk-likesubstrates for a recording medium using a brush comprising: providing aplurality of pieces of disk-like substrates for a recording mediumhaving a circular hole at the central portion thereof thereby forming aninner peripheral end surface, and stacking them while aligning thecircular holes to form an object to be polished having the circular holeat the central portion thereof; bringing a polishing material slurrycontaining a polishing material into contact with said object to bepolished; inserting a polishing brush having brush hairs stud on theperiphery of a rod-like shaft into the circular hole of said object tobe polished in a state where said slurry is brought into contact withsaid object to be polished, and rotating the polishing brush with theshaft as a center axis to polish the inner peripheral end surfaces ofthe substrates; wherein said polishing material slurry is controlled toremain at a constant temperature.
 2. The method of polishing using abrush according to claim 1, wherein the polishing brush is rotated andis reciprocally moved in a direction of inserting the brush relative tothe object to be polished to effect the polishing.
 3. A method ofproducing disk-like substrates for a recording medium including a stepof effecting the method of polishing using a brush according to claim.4. A substrate produced by the method of producing disk-like substratesfor a recording medium of claim
 3. 5. A method of producing a magneticrecording medium including a step of effecting the method of polishingusing a brush of claim 1.